Conformational model for the consensus V3 loop of the envelope protein gp120 of HIV-1 in a 20% trifluoroethanol/water solution

Based on experimental NMR data, a model was generated for the conformation of the disulfide-bond-closed cyclic peptide corresponding to the whole V3 loop of the consensus HIV-1 strain in a 20% trifluoroethanol/water solution. The obtained family of structures shows a prominent and well-defined amphipathic α helix at the C-terminal end of the peptide from Thr23 to Gln32. A series of turns characterizes the central Gly15–Tyr21 region, while the N-terminal region is poorly defined. Independent experimental data confirms the features of this model, and suggests that this type of conformation can be readily adopted when the V3 loop is in contact with a membrane. The examined V3 loop belongs to a macrophage tropic strain, and using the model, a structural explanation is proposed for the different requirements of V3 loops belonging to macrophage and T-cell line tropic HIV-1 strains.